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Which database sql did you dump? Was is the demo_db.sql or the empty_db.sql. based on the error I think u dumped the demo_db.sql, so go to the folder application/config/database.php and then change this
$db['default']['database'] = 'hospital_hmssell';
to
$db['default']['database'] = 'hospital_hms';

because the database name for the demo is called "hospital_hms" and the database for empty_db.sql is called "hospital_hmssell" so you're just using the wrong database name. I hope this helps.